This application claims the priority benefit of Taiwan application serial no. 89120196, filed Sep. 29, 2000.
1. Field of Invention
The present invention relates to a photomask structure. More particularly, the present invention relates to a photomask structure with an anti-electrostatic-discharge (Anti-ESD) ability.
2. Description of Related Art
Typically, the semiconductor process comprises four modules including the diffusion module, the etching module, the thin film module and the photo module. The photo module, in which the photolithography process is performed, is used to replicate the etching patterns for the etching module or implanting patterns for the thin film module on the photomask onto the wafer. Hence, the quality of the semiconductor device depends on whether the resolution of the photolithography process is good.
Currently, the photomask is formed of an insulating material such as quartz and surface covering materials such as Cr and MoSi. While the photomask is situated under an unexpected applied electric field, the patterns on the photomask are polarized easily.
However, with the increasing of the integration of the integrated circuit, the density of the pattern on the photomask is increased and the pitches of the bit line and the word line, and even the diffusion region and the capacitance, are decreased. Hence, the charges accumulating on the patterns because of the polarization will be easy to discharge as an electrostatic discharge effect while the space between the patterns is getting smaller and smaller.
Since the electrostatic discharge happens with emitting heat and energy, the local metal patterns on the photomask where ESD happens are melted and distorted by the high temperature. Therefore, the exposure result is worse.
The invention provides a photomask structure with an anti-electrostatic-discharge (Anti-ESD) ability. The photomask structure comprises a photomask, a conductive dust pellicle, a conductive frame and a conductive film. The photomask possesses a first surface and a pattern is located on the first surface. The conductive dust pellicle is coupled with the photomask through the conductive frame and the pattern is enclosed by the conductive dust pellicle, the conductive frame and the photomask. The conductive film covers the surface of the photomask uncovered by the conductive dust pellicle and the conductive frame. The conductive dust pellicle, the conductive frame and the conductive film constitute an entire conductive structure enclosing the surface of the photomask.
According to the Gauss law, the charges only distribute on the surface of a conductor and the object and the space inside the conductor will not be affected by the applied electric field and applied charges. The theorem indicates that a closed conductive shell can provide a shielding effect so that polarization effect happens only on the surface of the closed conductive shell such as the conductive structure covering the surface of the photomask while the photomask structure is located under an applied electric field. The conductive structure can protect the patterns on the photomask from being polarized by the applied electric field and the applied charges. Hence, the electrostatic-discharge problem can be overcome no matter how high the integration is and how dense the pattern is.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.